Sound quality
 
These are the headphones that showed me the difference of the sound of headphones driven by an integrated audio card and the ones driven by a dedicated one (in my case, Asus Xonar D1). Needless to say, it was absolutely massive. CAL! have fantastic mids, which make every uplifting trance track SHINE (try e.g. Phillip Alpha - Sudden Changes or Andy Blueman - Neverland). But in order to experience that, a dedicated audio card is a must. I'm pretty sure that they'll satisfy anyone that listens to ambient or orchestral music, at least as long as you're looking for fun-sounding headphones (they're V-shaped, but only slightly - at least to a basshead like myself).
 
They have rather decent midbass but little subbass which, I guess, is a price that needs to be paid if you want great mids. If you listen to dubstep, well... stay away from those, lol.
 
Comfort and isolation
 
They're decently comfortable. The cups are too small to cover my ears completely, which worsens the isolation, and probably the comfort as well.
 
Build quality, cord and looks
 
The build quality is bad. CAL! are made of plastic that has questionable quality, and after a couple of months I had to tape one of the headphones to the headband (where they join). The cord is also of questionable quality and is way too short for my taste (forget about using these with a PC that has the audio card inside the case). I think it'd also be better if CAL! had one cord that comes out of one of the headphones, rather than two cords that join below (in my case, a bit too close to my chin).
 
To me, CAL! look decent.
 
Conclusion
 
As I said, if you're looking for reasonably cheap and fun-sounding headphones for uplifting trance (possibly also ambient/orchestral music), these are the ones.

These are sometimes recommended for 'people who want lots of bass'. Well, I'm certainly one of those, and to me, DT-150 had hardly any bass at all. You can't feel the subbass; and when you EQ them to the point that the subbass is strong enough to be felt consistently throughout the whole song, it's still not perfect, and other frequencies suffer - as if their price was $5. I listen to trance and house, and can't stand hearing my favorite tracks without proper bass. My soundcard was Asus Xonar D1, so it's not like it couldn't drive DT-150 at all. Surely, I could've bought something better than Xonar D1, but I bet it wouldn't make much difference as far as the subbass is concerned. However, I'm happy to stand corrected if someone proves to me that that wouldn't be the case.
 
As far as the mids and highs are concerned, I had no problem with them, and was happy that the vocals weren't hissing (persistent problem with Ultrasone HFI-580, which I had before DT-150). But that is not what I bought these for - I'd exchange somewhat hissing vocals for quality subbass any day of the week.
 
They're made like a tank - durable, but look really ugly. Not that it's very important, just saying.
 
Overall rating: 4/5. I rate the bass 1/5, as DT-150 are sometimes misrepresented as 'bassy headphones', which they aren't. Not by any basshead standards.
 
If you like to feel the subbass, stay away from those, as they'll be nothing short of a let-down.

Introduction
 
Hi. Here's my short review of Ultrasone HFI-580. I'm not a professional writer and English isn't my native language, so bear that in mind.
 
My sound card: Asus Xonar D1
Music I listen to: trance (uplifting, progressive, tech), house (progressive, tech). Sometimes I also listen to hard trance, drum & bass and dubstep.
 
Dr. Bass-yl and Mr. Let's Hyde the Lows
 
During the first week I was overwhelmed with the amount of bass and its superb quality. Then they gradually got loose and lost much of their bass. It totally killed the pleasure of listening to bass-heavy tracks like Cosmic Gate - Ultra Curve or Nitrous Oxide - Magenta, which went from 'this is like an EARTHQUAKE' to 'this is nothing special, I'd rather do something else that listen to this'. It also killed the pleasure of listening to rather bass-light tracks like Aly & Fila - Khepera (Leon Bolier remix), at least to an extent. Very strangely, sometimes (like 1 in 30 cases) they sounded just like they should, and the bass was insane. I don't need 'moody' headphones - they need to be consistent! Some time later, I bought them again, and had the very same issue as with the previous cans - except that those were loose from the very beginning, and have never gotten to 'change their mood', as I returned them a few days later.

I had the exact same problem with AKG K81 DJ. The first week - the bass was great. Then they got loose, which killed much of the bass and most of the pleasure of listening to music. A couple of years later I bought another pair, and it was loose from the get-go and, of course, didn't provide enough bass to my liking. Am I cursed or what?
 
Problem with hissing

The inconsistent quantity of bass is the only reason that I'm giving these the lowest possible rating. If the bass were consistently powerful, I'd give these 4,5/5. Why only 4,5/5? They have a hissing problem, which made singers sound as if they had a lisp; this also made listening to e.g. the beginning of Cosmic Gate - London Rain (Back 2 Back 4 redub) physically painful. On the other hand, that's probably the only track with which there was such a problem. I strongly prefer music without vocals, so that was never a major issue.
 
Comfort

They were as comfortable as one could reasonably expect from bass-heavy headphones; my issue was that the clamp was very often too weak to provide enough bass - see above. Shame on you, Ultrasone, for such a poor design. Before you ask: yes, I tried using a rubber band on the first pair. For 2 days. It made them looser than before, which I found comical.
 
They have a very long cord, which to me was comfortable - I could walk around the room without worrying about the headphones falling off my head. However, it's a double-edged sword - if you're looking for portable headphones, the length of HFI-580's cord is going to be a major issue.
 
Looks
 
Definitely the least important topic, but they look decent. No issues here.
 
Conclusion
 
If you want consistent powerful bass, do not buy these, as you may as well have the same problems as I and some other people (search for the thread 'Ultrasone HFI-580 too loose?' - the HFI-780 model is also mentioned there, so watch out for that one as well) had. It is scandalous that you should pay over $100 for something so flawed.